iOS: add UIView category to get the QWindow it represents

Adding a simple way to get the QWindow pointer from any UIView
makes writing code where you only have UIView pointers a bit easier.

Perhaps we should also investigate if it is worthwhile to make
this category public to the application, to further enhance
working in a mixed environment.

Change-Id: Ic263003dc7683a8d976024cbbbc2558e8472a790
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>

src/plugins/platforms/ios/qioswindow.h

@@ -49,6 +49,10 @@
 class QIOSContext;
 class QIOSWindow;
 
+@interface UIView (QIOS)
+@property(readonly) QWindow *qwindow;
+@end
+
 QT_BEGIN_NAMESPACE
 
 class QIOSWindow : public QPlatformWindow

src/plugins/platforms/ios/qioswindow.mm

@@ -209,6 +209,17 @@
 
 @end
 
+@implementation UIView (QIOS)
+
+- (QWindow *)qwindow
+{
+    if ([self isKindOfClass:[EAGLView class]])
+        return static_cast<EAGLView *>(self)->m_qioswindow->window();
+    return nil;
+}
+
+@end
+
 QT_BEGIN_NAMESPACE
 
 QIOSWindow::QIOSWindow(QWindow *window)